1. Field of the Invention
This invention relates generally to magnetic writing on a magnetic medium where a magnetic layer to be written upon is stressed by the electrostriction of an adjacent electrostrictive layer and the electric field producing the electrostriction and the magnetic field producing the writing are both simultaneously generated by a recording head.
2. Description of the Related Art
Magnetic recording at area data densities of between 1 and 10 Tera-bits/in2 (Tbpsi) involves the development of new magnetic recording mediums, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect by the use of magnetic recording mediums with high magnetic anisotropy that can still be written upon by the increasingly small write heads required for producing the high data density. The problem has two conflicting requirements: 1. the need for a stronger writing field that is necessitated by highly anisotropic magnetic mediums and; 2. the need for a smaller write head to produce the high a real write densities, which write heads, disadvantageously, produce a smaller field gradient and broader field profile. Satisfying these requirements may be a limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that is the case, further increases in recording area density may not be achievable within those schemes.
The prior art “assisted-recording” schemes being applied to the mitigation of the above problem share a common feature, which is to pump energy into the magnetic system through the use of physical methods that are not directly related to the magnetic field produced by the write head. If such an assisted recording scheme can produce a medium property profile to enable low-field writing localized at the write field area, high data density recording can be achieved by even a weak write field as a result of the multiplicative effect of the spatial gradients of both the medium property profile and the write field. However, these prior art methods either involve deep sub-micron localized heating by an optical beam or ultra-high frequency AC magnetic field generation, both of which are expensive, complicated and inefficient to produce.
Referring to FIG. 1 there is shown a schematic, vertical-plane cross-sectional illustration of a prior art perpendicular recording system. The perpendicular recording medium (10) includes a magnetic recording layer, (1), a magnetically soft underlayer (SUL) (2) and an interlayer (3). The magnetic recording (write) head (20) comprises a write coil (4), a pole-tip (5) and a yoke/return pole (6). During the recording process, the write coil (4) is energized by an electrical current that induces a magnetic field whose flux lines are concentrated by the yoke/pole structure. The pole tip (5) concentrates these flux lines still further, producing a locally high density of flux lines in the recording layer (1) beneath the pole tip. The SUL (2) acts as a magnetic imaging layer for the writer, which both enhances the magnetic field produced in the recording layer at the pole tip and also provides a return path for the magnetic flux to the rear portion of the yoke/return pole producing a closure of the flux lines. An inherent problem in the recording scheme as exemplified by this figure is that as the size of the pole tip (5) decreases to increase the recording density, the magnetic field produced in the recording layer at the pole tip position decreases in amplitude, which causes a loss of writability and increases in lateral spread, which causes interference with neighboring bits and, thereby, decreases achievable data density.
For thermal-assisted magnetic recording, also known as heat-assisted magnetic recording (HAMR), an optical laser beam is directed onto the write head. By passage through an optical waveguide and a near-field antenna, the optical energy is focused into a deep sub-micron size optical spot on the recording layer (1) close to the pole-tip (5), where the write field profile of the pole-tip overlaps with the optical spot. The optical energy delivered to the recording layer heats up the layer locally. The temperature rise produces a decrease in the magnetic anisotropy of the recording layer material and the magnetization of the recording layer grains becomes more easily switched by the write field. With the optically created medium anisotropy profile overlapping with the writer field profile, the effective write field spatial gradient can be significantly enhanced due to the multiplicative effect of the thermal and magnetic field gradients. Thus, recording can be achieved with the lower magnetic write field of the smaller write head with a resulting higher recording density.
For ferromagnetic-resonance-assisted magnetic recording, also known as microwave-assisted magnetic recording (MAMR), an AC magnetic field in the frequency of tens of Giga-Hz (GHz) is imposed upon the location of the recording medium where the write head reverses the magnetizations of the magnetic recording layer (1). When the frequency is close to the ferromagnetic resonance (FMR) frequency of the magnetization of the magnetic grains in the recording layer (1), energy can be pumped into the magnetic medium grain magnetizations to bring them into an FMR mode, which leads to their switching by a much lower write head field than would otherwise be required. With the medium FMR having a high quality factor, i.e., at a given AC field frequency, the highest FMR occurs at a given reversing field and decreases quickly as the field deviates from that value (sharply peaked frequency dependence of FMR), the write field gradient can also be effectively enhanced and higher write densities can be achieved at lower fields.
The binary-anisotropy-assisted magnetic recording (BAMR) is similar to HAMR. In this scheme an antiferromagnetic-ferromagnetic (AFM-FM) transitional layer is formed beneath the uppermost perpendicular-to-plane high-anisotropy recording layer and another, lower, high anisotropy layer having in-plane anisotropy is formed beneath the transitional layer. Upon local heating, the AFM-FM switches from its AFM phase to its FM phase and exchange couples the upper high anisotropy recording layer to the lower high anisotropy layer. Thus the locally heated area acts similarly to a single magnetic domain with two high-anisotropy axes that are perpendicular to each other. The in-plane anisotropy of the lower layer makes the magnetization of the upper recording layer easier to switch. With the heating gradient profile effectively multiplying the write-field gradient, the effective write-field gradient is enhanced as it is in HAMR.
The existing assisted-recording schemes discussed briefly above have a common feature, the pumping of energy into the magnetic system by means other than directly increasing the magnetic write field of the write head. However, as already mentioned, these methods all are expensive, complicated and energetically inefficient. What is needed and what the present invention will provide, is an easy and effective transition from conventional perpendicular magnetic recording to an assisted form of magnetic recording in which the assistance methodology requires less complication of existing head-manufacturing processes and relies on a physical property of the recording system that is more easily controlled.